Field of the Invention
The invention relates to a method for checking analog sensors which cyclically acquire measurement signals that are representative of operating conditions of an internal combustion engine. The measurement signals are fed to a controller of the internal combustion engine for further processing and the sensors are evaluated in regard to the plausibility of the measurement signals on a basis of measured values in a predetermined time period.
With the increasing use of electronics in motor vehicles, the number of built-in sensors and sensor systems is also growing not only for the straightforward traveling functions but also for safety functions, for protecting the environment and for luxury features. By use of an electronic control unit which obtains its information from these sensors, suitable measures required for the operation of the internal combustion engine are taken, such as, for example, regulation of the ignition and of the fuel injection. In order to ensure optimum utilization of the fuel with the smallest burden on the environment and maximum traveling comfort, the intake air temperature and, in particular, the temperature of the coolant of the internal combustion engine are detected, inter alia, by analog temperature sensors. Since the output signals of these temperature sensors influence both the engine management and the exhaust gas management, the temperature sensors must be checked with regard to their functionality.
Published, Non-Prosecuted German Patent Application DE 33 28 450 A1 discloses a method for checking measurement sensors which acquire electrical measurement signals that are representative of the operating conditions of an internal combustion engine and are statically monitored in a checking unit. The measurement signals of the operating parameters of the internal combustion engines are acquired cyclically and checked with regard to their measured value change from one interrogation cycle to a succeeding interrogation cycle, and are accepted only when the measured value change lies within permissible limits. Stochastic interference is masked out of the measurement signal, recorded and tolerated up to a practical limit. If an erroneous measurement signal is identified, an emergency procedure that counteracts this fault is activated. Such a method makes it possible to ascertain whether the sensor output signal is within a plausible range of values. sensors, in particular temperature sensors, under certain circumstances exhibit a sporadic behavior such that the sensor output signal jumps to a constant value within the plausible range of values. This fault may even remedy itself. The known gradient test can detect these jumps only when they occur during the operation of the electronic controller that evaluates the output signal of the sensor. If the fault occurs with the controller switched off, it is not identified. In a subsequent operating phase, that is to say when the internal combustion engine is restarted, the value, which is now constant, of the output signal of the sensor is considered to be in order. On account of the incorrect information, the internal combustion engine is not controlled or regulated optimally, which can lead to elevated exhaust gas emissions, in particular.
It is accordingly an object of the invention to provide a method for checking analog sensors which overcomes the above-mentioned disadvantages of the prior art methods of this general type.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for checking analog sensors that output measurement signals representative of operating conditions of an internal combustion engine, which includes:
during a first traveling cycle after a start of the internal combustion engine, checking to see if a positive change in a measurement signal of an analog sensor has occurred if an initial measurement signal of the analog sensor lies below a predetermined threshold value when the internal combustion engine is started; and
entering a fault entry into a fault memory if, within a predetermined time period, the positive change in the measurement signal, expressed as a difference between the initial measurement signal when the internal combustion engine was started and a present value of the measurement signal when the predetermined time period has elapsed, does not reach an expected value.
After the start of the internal combustion engine, a check is made to see whether a positive change in the measurement signal is established if the measurement signal lies below a predetermined threshold value when the internal combustion engine is started. A fault entry is made if, within a predetermined time period, the change in the measurement signal, expressed as the difference between the measurement signal when the internal combustion engine is started and the present value of the measurement signal when the time period has elapsed, does not reach an expected value.
Since the possibility of the fault being remedied is no longer afforded in this traveling cycle, a check is made during the succeeding traveling cycle to see whether the absolute value of the change in the measurement signal exceeds the expected value within the predetermined time period. If this is the case, then the fault is deemed to have been remedied. Sporadically occurring faults can thus be reliably distinguished from permanently occurring faults, as a result of which it is possible to prevent sensors from being replaced unnecessarily.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for checking analog sensors, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.